Recirculating ball screw

ABSTRACT

A recirculating ball screw suitable for high speed operation and having an improved lubrication system is disclosed. Recirculation of the balls is accomplished in a smooth and continuous manner by a new ball recirculating member which cooperates with the lead screw to urge the balls out of their normal ball track to transfer the ball over the lead screw in an axial direction and then deposit the ball smoothly back into the ball track without the use of ball pick-up fingers protruding into the ball track. The improved lubrication system is comprised of an outer sleeve which seals the lubricant in place by the use of sealing rings so as to prevent lubricant contamination and unwanted lubricant migration.

United States Patent Wysong [451 June 6, 1972 [54] RECIRCULATING BALLSCREW [72] Inventor: Paul V. Wysong, Northridge, Calif. [73] Assignee:Schrillo Company, Sepulveda, Calif.

[22] Filed: Dec. 9, 1970 [21] Appl. No.: 96,340

FOREIGN PATENTS OR APPLICATIONS 880,001 10/ 1961 Great Britain ..74/4S9Primar'y Examiner-Leonard I-I. Gerin At!0rney-Spens1ey, Horn & Lubitz[57] ABSTRACT A recirculating ball screw suitable for high speedoperation and having an improved lubrication system is disclosed.Recirculation of the balls is accomplished in a smooth and continuousmanner by a new ball recirculating member which cooperates with the leadscrew to urge the balls out of their normal baII track to transfer theball over the lead screw in an axial direction and then deposit the ballsmoothly back into the ball track without the use of ball pick-upfingers protruding into the ball track. The improved lubrication systemis comprised of an outer sleeve which seals the lubricant in place bythe use of sealing rings soas to prevent lubricant contamination andunwanted lubricant migration.

7 Claims, 9 Drawing Figures [52] US. Cl. ..74/424.8 R, 74/467 [51]lnt.CI .Fl6h l/l8,Fl6h 55/22,Fl6h 57/04 [58] Field of Search ..74/459,424.8 R, 467

[56] References Cited I UNITED STATES PATENTS 2,895,343 7/1959 Omer..'......74/459 2,714,821 8/1955 Omer ....74/459 2,851,897 9/1958Cochrane ....74/459 3,592,072 7/1971 Nilsson ..74/459 I I I F I I e s II i I I I I J I, I F

LJ I RECIRCULATING BALL SCREW BACKGROUND OF THE INVENTION 1. Field ofthe Invention This invention relates to the field of recirculating ballscrews.

2. Prior Art Recirculating ball screws are well known in the prior artfor the conversion of an angular rotation to linear translation andconversely linear translation to angular rotation. A typical applicationis in the flap actuating mechanism used in many modern jet aircraft. Insuch an application, the lead screw may be supported on bearings and isdriven by a reversible motor. The nut of the recirculating ball screw isattached to the flap, as are other linkages which support the flapthroughout its travel. By running the motor in one direction, the nutadvances onthe lead screw, thereby forcing the flap towards its extendedposition. Reversing the motor will reverse the direction of travel ofthe nut with respect to the lead screw, thereby urging the flap towardits retracted position.

Recirculating ball screws are capable of creating very high forces witha minimum of friction and wear and, therefore, are usually driven by amotor through a reduction gear, so as to take full advantage of theforce creating ability of the ball screw. Because of the reduction gear,the angular velocity of the driving member of the ball screw, usuallythe lead screw, is relatively low and, consequently, prior artrecirculating ball screws which had a' relatively low maximum operatingangular velocity were still useful in such applications. However,operation of the prior art recirculating ball screws at higher angularvelocities would result in a sudden and premature failure of the ballrecirculating mechanism, for the reasons hereinafter described.

Recirculating ball screws are comprised of a lead screw, a nut, aplurality of balls and one or more ball recirculating members. The leadscrew has a helical ball track or groove with a cross-section very muchlike the cross-section of the inner race of an annular contact ballbearing. Similarly, the nut contains a helical ball groove or track withthe same lead as the lead screw, and again, with a cross-section muchlikethe cross-section of an outer race of an annular contact ballhearing. The ball recirculating member or members pick the balls out oftheir normal track, defined by the lead screw and nut, transports themaxially, and deposits them at a new location along the lead screw, so asto retain and recirculate the balls in their desired trajectory.

Prior art recirculating ball screws had either internal ballrecirculation, that is, ball recirculation within the lead screw, orexternal ball circulation, that is, ball circulation on or within thenut. In either case, ball recirculation is accomplished with the use ofa finger which extends into the helical ball path so as to intercept theballs, one at a time, and lift them out of the load path into the ballrecirculation channel, which directs the balls in a generally axialdirection and redeposits the balls at a second axial location forrecycling through the helical ball path between the nut and lead screw.The balls approaching the pick-up finger follow a generally helical pathdefined by the rolling of the balls in the helical ball tracks of thelead screw and nut, and on striking the pickup finger, are redirected soas to have a substantial impact force to direct the balls out of thishelical ball path and to recycle them to a new position on the ballscrew. Because of the abrupt change in direction of the ball caused bythe pickup finger, the ball pick-up finger must have sufficient strengthand toughness to resist Brinelling and/or fatigue. For low speedoperation, the forces with which the ball strikes the ball pick-upfinger are quite low and a ball pick-up finger of sufficient toughnessmay readily be made to achieve a reasonable life and reliability.However, if the speed of operation of the ball screw is increased, boththe force with which the ball strikes the ball pick-up finger and thefrequency of such striking increases, so that even at moderate speeds,the increased frequency of impingement causes premature fatigue failureof the pick-up finger resulting in total failure of the recirculatingball screw.

The forces with which the ball strikes the ball pick-up finger in theprior art recirculating ball screws can be reduced by reducing theabrupt angular change in the ball path from the helical path in the ballscrew to the path defined by the ball pick-up finger, that is, by makingthe ball pick-up finger more nearly tangent to the helical ball path.However, to do this, a longer and thinner ball pick-up finger must beused, so that the net result is that the reduction in forces between theballs and the pick-up finger is offset by the reduced structuralintegrity of the ball pick-up finger because of its increased length.Consequently, satisfactory higher speed .operation is not achieved bymaking such a change in the design of the pick-up finger.

Prior art recirculating ball screws generally do not have any specialprovisions for lubrication. In many of these ball screws, the ballpick-up finger is an extension of the ball recirculating conduit and,therefore, the material for the recirculating conduit is selected basedon the structural requirements'for the ball pick-up finger. Also,generally the recirculating conduit or conduits consist of one or morerecirculating members which attach to the nut and recirculate the ballsthrough a conduit outside the nut. These recirculating members do notreadily lend themselves to lubrication, other than by the placing oflubricant on the lead screw over which the nut travels. In someapplications, the lead screw is readily lubricated and,

therefore, the absence of a supply of lubricant and a method fordispersing it within the nut is nota limiting factor, but in otherapplications, such as in flap actuators for modern aircraft aspreviously described, such a supply of lubricant is not readilyachieved. Therefore, life and reliability of the recirculating ballscrew in such an application depends at least in part for the ball screwto retain its own lubricant supply.

In other applications, both high speed and high temperature operation isnecessary. By way of example, modern jet engines have thrust reversingmechanisms attached thereto; such mechanisms having doors or cascadeswhich, when actuated, redirect the exhaust of the engine to reverse thedirection of thrust of the engine. These doors must be moved betweentheir normal and their thrust reversing positions, very quickly, foreffective aircraft declarations. Thus, a recirculating ball screw forsuch applications 'mustbe reliably capable of high speed operation. Inaddition, the environment in the region of a jet engine exhaust isnecessarily of elevated temperature; temperatures as high as 600F in thecompartments for such equipment not being unusual. Prior artrecirculating ball screws, because of their inherent limitations aspreviously discussed, are not suitable for such applications.

BRIEF SUMMARY OF THE INVENTION The present invention is a recirculatingball screw suitable for high speed and high temperature operation andhaving an improved lubrication system for insuring life and reliabilityunder such conditions. Satisfactory high speed operation is achieved bya new ball recirculatingmember which directs the balls from the helicalball track without the use of a ball pickup finger. The ballrecirculating member, in combination with the lead screw ball groove,urges the balls radially outward from the lead screw in a directioninitially substantially tangent to the helical ball path, and aftertransmitting the balls axially along the lead screw, redeposits theballs in the helical ball track in a direction again substantiallytangent to that path. In this manner, sharp bends in the direction ofthe ball path are eliminated and, therefore, the high impingement loadson the balls and ball recirculating member characteristic of the priorart recirculating ball screws are eliminated.

The improved lubrication system for the present invention recirculatingball screw is achieved through the use of selected materials andlubricants for the ball recirculating member and by an outer sleeve orsealing member which envelops the ball recirculating member and, incombination with appropriately located sealing rings prevents loss ofthe lubricant and ingress of contaminants.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of aprior art recirculating ball screw.

FIG. 2 is a cross-section of the recirculating ball screw of FIG. 1taken along lines 2-2 of that figure.

FIG. 3 is a cross-section of the recirculating ball screw of FIG. 1taken along lines 3-3 of that figure.

FIG. 4 is a perspective view of the present invention recirculating ballscrew partially cut away to show the ball recirculating members.

FIG. 5 is a cross-section of the recirculating ball screw of FIG. 4taken along lines 5-5 of that figure.

FIG. 6 is a cross-sectional view of the recirculating ball screw of FIG.4 taken along lines 6-6 of thatfigure.

FIG. 7 is a view of the ball recirculating member showing the axial ballpath within the recirculating member.

FIG. 8 is an exploded view of a cross-section of the lead screw and ballrecirculating member showing the forces on the balls caused by the ballrecirculating member which urge the ball .out of the lead screw groovefor recycling by the recirculating member.

FIG. 9 is a perspective view, partially cut away, of an alternateembodiment of the present invention having a single ball recirculationmember with a plurality of ball recirculation paths.

DETAILED DESCRIPTION OF THE INVENTION Referring first to FIGS. 1,2 and3, a perspective view of a prior art recirculating ball screw may beseen. The major elements of this recirculating ball screw are the sameas the major elements in the present invention ball screw, though designchanges, particularly in the recirculating member, have been made toachieve the results of the present invention device, The recirculatingball screw is comprised of a lead screw 10, a nut 12, recirculatingmembers 14, and a compliment of balls 16 which are located between ballgrooves in lead screw 10 and nut 12 and are continually recirculated byrecirculating members 14 so as to never pass out from under nut 12.

The ball groove in the lead screw 10 and in nut 12 are very much likethe raceways of the well known annular contact ball bearing, but arehelical, rather than annular as in the ball bearing. The ball grooves inlead screw 10 and in nut 12 have the same lead and are so disposed so asto define a helical ball groove or path between lead screw 10 and nut12. A full compliment of balls 16 is placed in this helical ball grooveand also within ball recirculating members 14 so that as the lead screw10 is rotated with respect to nut 12, the lead screw advances withrespect to the nut by rolling on the balls between the lead screw andthe nut. As the balls approach the end of their helical path, they areremoved from this helical path by the ball return members 14,transferred axially through the ball return members, and deposited at apoint in their helical path forward of where they were picked up.Rotation of the lead screw 10 in the opposite direction reverses thedirection of the balls within their helical ball path and also reversesthe direction of balls within the ball return members 14, so as toalways confine the balls within the ball return members 14 or within thehelical ball groove in lead screw 10 and nut 12 between the ends of ballreturn members 14.

Also shown in FIG. 1 are a threaded area and a shoulder 22 on nut 12,which may be used for mounting. Normally, one member of the ball screw,such as nut 12, is mounted so as to be restrained in rotation and theother member, in most cases the lead screw 10, is mounted on bearings 20and is driven by a reversible rotating motor so that operation of themotor in a chosen direction causes the nut to advance along the leadscrew.

Now referring to FIGS. 2 and 3, further details of the prior art ballrecirculating members 14 may be seen. This explanation of a typicalprior art recirculating member is presented here so as to make moreapparent the novel features of the present invention recirculating ballscrew, and in particular, the ball recirculating methods used therein.In FIG. 2, recirculating member 14 contains ball pick-up finger 24,which extends into the helical ball groove between nut 12 and lead screw10 so as to interrupt the helical ball path of the balls and to redirectthe balls into ball recirculating member 14. It may be seen that thehelical ball path, generally indicated by dashed line 26, is interruptedat point 28 and abruptly changed to ball path 30 through ballrecirculating member-14. The abrupt change in ball path direction atpoint 28 is caused by the impingement of the balls on the ball pick-upfinger 24, and because of this abrupt change in ball direction, the ballpick-up finger 24 is subjected to high impact loads even at moderateangular velocities of lead screw 1 FIG. 3 shows the other end of ballrecirculating member 14 and the manner in which the balls areredeposited to the helical groove between lead screws 10 and nut 12. Itmay be seen that the balls undergo a similar abrupt change in directionof motion at point 32, which results in high loads on the balls and leadscrew 10 at that point. Also shown is a ball pick-up finger 34substantially identical to the ball pick-up finger 24 in FIG. 2, whichserves as a guiding finger in redepositing the balls, as shown in FIG.3, and which further acts as a ball pick-up finger when the lead screwis rotated in the opposite direction. Consequently, rotation of the leadscrew at a high angular velocity in the direction indicated by thearrows in FIGS. 2 and 3 will cause a deterioration and failure of ballpick-up finger 24, whereas a rotation of lead screw 10 at a high angularvelocity in the opposite direction will cause a similar deteriorationand failure in ball pick-up finger 34.

It should be further noted that in the prior art lead screw of FIGS. 1,2 and 3, there has been no effective method for retaining and uniformlydispensing lubricant.

Now, referring to FIG. 4, a partially cut away perspective view of thepresent invention recirculating ball screw may be seen. The principalelements of this recirculating ball screw are substantially the same asthe principal elements of the recirculating ball screw shown in FIG. 1.By way of example, lead screw 40 is very similar to lead screw 10 shownin FIG. I, having only minor differences, the details of which will besubsequently described. Consequently, FIG. 4 shows only those elementsand details of the present invention ball screw which are inventive innature, and does not show those parts of the ball screw which are wellknown in the prior art, such as the ends of lead screw 40 which areadapted to mount the lead screw in a particular installation.

The lead screw 40 is a generally cylindrical member defining acontinuous helical ball groove. The nut 42 which is disposed about thescrew 40 is generally a cylindrically shaped member having an annularcross-section and defining an internal continuous helical ball groove.The ball grooves of the screw 40 and nut 42 are adaptable tocoooperatively engage balls between them. A plurality of recirculatingmembers 44 are disposed axially along the nut 42. Each recirculatingmember 44 comprises a rectangular section which has a surface facing theinterior of the nut 42. A tunnel is disposed within each member 44defining a pair of openings terminating in the interior of the nut 42.Each tunnel defines a path .or trajectory such as that shown in FIG. 7,one opening of which urges a ball out of a groove into the tunnel. Thetunnel carries the ball over a land and deposits the ball from the otheropening into an adjacent groove. Thus, by the use of a plurality ofrecirculating members 44 the balls between the screw 42 and nut 40 arecontinuously recirculated. The action by which the ball is urged fromone groove and over the land is discussed in detail herein. The screw40, nut 42 and recirculating members 44 may be metal parts madeutilizing known machining techniques.

In the preferred embodiment, as shown in FIG. 4, three ballrecirculating members 44 are disposed apart around nut 42, and arespaced axially along the nut so that each of ball recirculating members44 operates with respect to an independent tum of the helical ballgroove in nut 42 and lead screw 40. It is to be understood, however,that the principles of the present invention may be readily adapted toother ball recirculating members, such as a ball recirculating memberwhich transfers the balls in an axial direction by more than one turn ofthe helical ball groove.

Now referring to FIG. 5, a cross-section of the present inventionrecirculating ball screw taken along lines 5-5 of FIG. 4 may be seen.The helical ball groove between nut 42 and shaft 40 defines a diameter52 for the normal helical path of the centers of the balls. Also shownin the figure is the trajectory of the ball centers as the balls travelthrough the ball recirculating member 44, generally indicated by thedashed line 54in that figure. Of particular importance to the presentinvention is the fact that the trajectory 54 for the balls as they passthrough the recirculating member 44 is substantially tangent to thecircle defined by diameter 52 at points 58 and 60, and that it smoothlyextends radially outward to point 62 where the ball is at a sufficientradial distance to clear the land between the grooves in lead screw 40(which define the lead screw outer diameter 56) so that the ball may beguided in a generally axial direction over the land for redepositing inthe helical groove on the opposite side of the land. Also, of importanceto the present invention, for reasons which will become subsequentlyapparent, is the fact that the outer diameter 56 of screw 40 is lessthan the diameter 52 (defining the path of the centers of the balls 46in the helical ball groove).

Now referring to FIG. 6, a cross-section along lines 66 of FIG. 4 may beseen. This cross-section shows in greater detail the geometry of leadscrew 40 and nut 42, and the disposition of balls within the helicalball groove between lead screw 40 and nut 42, and in ball recirculationmember 44.

For purposes of illustrating the manner in which the balls contact andare free to rotate on the lead screw 40 and nut 42, it has been assumedin FIG. 6 that the lead screw 40 is sub jected to a rotating forceurging it towards the left of that figure, and in opposition to thisforce a restraining force has been applied to the nut 42. These forcesare generally indicated by the arrows in that figure.

When the recirculating ball screw is subject to the loads as shown, thelead screw 40 moves to the left with respect to nut 42, to the extentthat it is free to do so. This contact is best illustrated by the fourballs which are shown contacting the cross-section of nut 42, and whichhave indicated through them diametral lines through the point of contactof the balls 46 with the lead screw 40 and nut 42. The diametral linesthrough the points of contact of the balls indicate the direction of theforces exerted by the balls on lead screw 40 and nut 42. The arrowheadon these lines indicates the direction of the force exerted by the balls46 on the lead screw. It is to be noted that these forces have both aradial and an axial component. When the direction of the load on leadscrew 40 and nut 42 is reversed, the screw 40 will move to the rightwith respect to nut 42, to the extent that it is free to do so, and thecontact points between the balls 46 and lead screw 40 and nut 42 willnow fall on the dashed diametral line indicated in FIG. 6.

In the presently preferred embodiment groove edge loadings are minimizedthrough controlled geometry of the helical path cross-section allowingthe use of a smaller than normal overland diameter. The controllingfactors are contact angle, individual ball load and location of themajor diameter of the ball contact ellipse with respect to groove comorradius of the screw member. The net effect of these factors is arelatively shallow ball groove in the lead screw, which smoothly blendsinto the outer diameter of the lead screw.

Now referring to FIG. 7, a view of the ball recirculating member 44,looking into the ball groove of that member, may be seen. Also indicatedin that figure is a projection 70 of the helix described by the centerof balls 46 as they travel in the helical ball groove between nut 42 andlead screw 40. The projection of this helix is indicated in that figureas the continuation of the path of travel of the center of the balls 46as they pass through the ball recirculating member 44, generallyindicated by the line 72 in that figure. It is to be noted that path 72at points 74 is substantially tangent to, and a continuation of, helicalpath 70, and that between points 74, path 72 curves so as to transferthe balls in an axial direction over a land of lead screw 40. A balllocated at point 62 is located directly over a land between grooves inlead screw 40, as indicated in FIGS. 5 and 6. The curve in ball path 72should be free of abrupt turns so as to avoid high acceleration forceson the balls as they move through the ball recirculation member 44, butotherwise may have any convenient geometry.

In the presently preferred embodiment, a specific curve'has been foundto be especially useful for the shape of the ball path projection 72.This shape consists of segments of a cycloid between points 74 and 62.The use of the cycloida] segments yields the following results. Sincethere is substantially a full complement of balls in the helical ballgroove between lead screw 40 and nut 42 and in the ball recirculationmember 44, the linear velocity of the balls along their path of travelis constant (for a constant angular velocity). Therefore, there is nolinear acceleration of the balls along their path. However, there is asignificant acceleration of the balls in a radial direction. Suchacceleration allows the balls to move first radially outward so as toclear the land in lead screw 40 and then to move radially inward so asto be redeposited in an adjacent lead screw groove as was shown in FIG.5.

In addition to the radial acceleration on the balls, another majorcomponent of acceleration is acceleration of the balls to achieve theaxial motion of the balls within the ball recirculating member 44. Thisacceleration is substantially perpendicular to the tangent of the arc ofthe path of travel 72 through the path of travel 72 through the ballrecirculation member 44, as shown in FIG. 7. By having the ball follow asubstantially cycloidal path this component of ball acceleration issubstantially constant as the ball travels through the recirculationmember 44.

In summary, it is to be noted that the path followed by a ball inrolling along the helical ball groove between lead screw 40 and nut 42,and in passing through the ball recirculating member 44, is a trajectorywhich, unlike that of the prior art recirculating ball screw shown inFIGS. 1, 2 and 3, is free of sudden changes in direction, and instead isa smooth and continuous trajectory over which the balls may roll, (e.g.,the ball trajectory defines a fair curve) without being subject todamaging accelerations as may occur in prior art recirculating ballscrews as the balls strike theball pick-up finger 24. Also, it is to beunderstood that substantially any relatively smooth curve may be usedfor the axial ball trajectory 72 in FIG. 7 or for the radial balltrajectory 54in FIG. 5 (e.g., so as to define a fair curve) withoutdeparting from the scope and spirit of the present invention. Inaddition, it is to be understood that it is not necessary for thevarious parts of the ball trajectories to be perfectly tangent to theadjoining ball trajectory, that is, trajectory 72 in FIG. 7 need not beperfectly tangent to trajectory 70 at point 74. Though any lack oftangency at such points will increase the loads on the balls and thesurrounding structure at that point, the lack of tangency will normallybe considerably less than that experienced by the prior artrecirculating ball screw at point 28 (FIG. 2), and in addition, therecirculating member 44 is much more able to withstand high ball loadsthan is the prior art recirculating ball screw, because of the absenceof a structurally weak ball pick-up finger. Furthermore, though thepresent invention recirculating ball screw-is capable of operation atspeeds unobtainable with the prior art recirculating ball screw, theadvantages of the improved lubrication system and the ball recirculationwithout the use of a ball pick-up finger makes the present inventionuseful and desirable in low speed applications also.

Now referring to FIG. 8, the manner in which the balls are encouraged(e.g., assured) to leave the ball groove in lead screw 40 may be seen.This figure shows a portion of lead screw 40 and ball recirculationmember 44 and the forces on a ball as the ball proceeds into the ballrecirculation member 44. Also shown in phantom in this figure is theoutlineof a ball groove in nut 42, and the normal contact of the ballwith that ball groove, as was pictured in and described with respect toFIG. 6. It may be seen that normally the ball contacs the ball groove inlead screw 40 at point 80, and on a point 82, diametrically oppositepoint 80, the ball normally contacts the helical groove'in nut 42.However, as the center of the ball moves along trajectory 70 in FIG. 7and passes point 74 so as to be within the curved portion of the balltrajectory within the ball recirculation member 44, the contact pointbetween the ball and the recirculation member 44 moves from point 82 toa contact point, which is closer to the lead screw, such as point 84(FIG. 8). This movement of the contact point is due to the geometryselected for the ball groove in the ball recirculation member 44 and thecurvature of trajectory 72 between points 74 and 76. As the contactpoint between the balls and the nut 42moves down from point 82, there isa resultant force on the ball tending to encourage the ball to moveupward into ball recirculation member 44 and over the land between ballgrooves on lead screw 40. By way of example, when the contact betweenthe ball and ball recirculation member 44 has moved down to point 84, itmay be seen that the force on the ball from the nut 42 (F,,) is nolonger colinear with the force on the ball from the lead screw 40 (F,and that the resultant of these two forces (F is a force tending to urgethe ball into the ball recirculation member 44 and over the land betweenball grooves in lead screw 40. As the ball trajectory in the ballrecirculation member 44 curves away from what would be a continuation ofthe helical trajectory 70 (FIG. 7) the pressure on the ball at points 80and 84 in FIG. 8 will further force the ball to move out of the ballgroove in lead screw 40 as hereinbefore described.

During the ball transfer through ball recirculation member 44 to anadjacent groove the forces acting on a ball as a free body are afunction of the helix' angle and the recirculating member geometry. Atpoint 74 the geometry of the ball groove inv the ball recirculationmember 44 is substantially a continuation of the helical .ball groove innut 42. However, since the ball recirculation member 44 is in generalnot intendedto aid in supporting the axial load applied to therecirculating ball screw, the ball path in recirculating ball member 44at point 74 is somewhat larger than the equivalent ball path in'nut 42so that the balls, which undergo a slight elastic deformation and whichelastically deform a contact area on nut 42 and lead screw 40 whenloaded therebetween, may enter the ball recirculation member 44 withoutsubjecting that member to similar loads and deformation. In addition, itis desirable to radius or otherwise slightly relieve the'ball groove innut 42 in the vicinity of ball recirculating member 44, so that theloads on the balls due to an axial load on the recirculating ball screware gradually relieved as the ball approaches the ball recirculatingmember 44,'and passage of a loaded ball over a sharp comer is avoided.

Now referring to FIG. 9, an alternate embodiment of the presentinvention recirculating ball screw, partially cut away, may be seen.'lnthis embodiment, a single ball recirculation member 90 is disposed infunctional relationship to the nut 92 in the same manner as each of theball recirculation members 44 shown in FIG. 4. This single ballrecirculation member 90 contains a plurality of ball recirculating pathstherein, each of Which is substantially the same as the ballrecirculating path in the ball recirculation members 44. With thisplurality of ball recirculating paths, adjacent portions of the helicalball groove between nut 92 and lead screw 94 may contain a fullcomplement of balls, since one ball recirculation path urges the ballsout of the helical groove before the adjacent recirculating pathdeposits additional balls into that same groove.

I In all the embodiments of the present invention heretofore described,the ball recirculation member urges the balls out of the helical ballpath and over a single land in the lead screw to deposit the balls inthe immediately adjacent ball groove. This limited axial transportationof the balls is easily accomplished through the use of a ballrecirculation member having the geometry and characteristics ashereinbefore described. However, it is possible using the principle ofthe present invention to axially transport the balls by more than oneball groove if such a variation in the present invention were desired.To achieve this, the ball recirculation member would be so adapted as tourge the ball out of the groove in the lead screw and then to graduallyenvelope the balls in a conduit to transport the balls radially outwardand axially over the helical ball groove in the nut, and to subsequentlydeposit the balls at any desired new axial location. 1

Having now described the mannerin which ball recirculation is achievedin the present invention recirculating ball screw, a description of theimproved lubrication system may now be given; Referring for this purposeto FIG. 4, it may be seen that ball recirculation members 44 fit withina mating opening of nut 42 and that an outer sleeve 48 slides axiallyover ball recirculation members 44 and nut 42 so as to retain the ballrecirculation members 44 in position and to provide a cover for theassembly. The volume between the outer surface of nuts 42 andrecirculating member 44 and the interior surfaces of sleeve 48 is usedas a lubricant reservoir. The ends of the reservoir are sealed with sealrings 50 which are located in mating grooves in nut 42 and incooperation with outer sleeve 48 provide an outer surface seal over nut42 and ball recirculation members. 1

The absence of a fingeraspart of the ball recirculation member and thecontrolled acceleration of a ball when in the ball recirculation member(and consequently the forces between a ball and the recirculationmember) allow a wider choice of materials and lubricants for therecirculating ball screw. One type of material which has been foundparticularly useful for recirculating member 44 are porous metals. Thesematerials have good structural integrity and dimensional stability, andprovide a means for uniformly transporting by capulary action lubricantfrom the reservoir to the balls. In the presently preferred embodimentthe lubricant is fluorsilicon fluid.

Having now described the preferred embodiment of the present inventionrecirculating ball screw and its improved lubrication system, manyvariations thereof will become apparent to one skilled in the artwithout departing from the scope and spirit of the present invention. Byway of example, the preferred embodiment of the present invention is anembodiment directed particularly tohigh speed and high temperatureapplications. However, recirculating ball screws are commonly used inmany applications which may involveex- I tremes in temperature,speedQload, moisture, contamination, etc., and variations of theheretofore described preferred embodiment will become immediatelyobvious to one skilled in the art of recirculating ball screws and ballbearings. By way of more specific example, in applications involving lowspeeds and moderate temperatures, ball path curvatures within therecirculating ball screw are less critical and other lubricants may befound to be better adapted to such environment. In applications whereinthe recirculating ball screw may be immersed in an adequate lubricant,or anadequate supply of lubricant furnished by some other means, theball recirculation member 44 might be fabricated from a substantiallynonporous material. These specific variations in application arementioned here for the sole purpose of illustrating a few'of thepossible variations which become apparent as a result ofa change inapplication of the present invention recirculating ball screw, and arenot intended to limit or restrict the present invention in any way.

I claim: l. A recirculating ball screw including a lead screw and nutdefining a helical ball path, comprising:

a plurality of balls; I a ball recirculating member, coupled to saidnut, said member defining at least one tunnel having a pair of openingstenninating in the interior of said nut such that one of said openingsis axially disposed from the other by a span of at least one land, saidtunnel defining a path over at least one land of said screw, saidopenings being shaped so as to apply pressure on said balls, urging saidballs out of the ball groove into said tunnel;

a housing disposed about said nut defining an enclosed reservoir for thestorage of a lubricant;

transport means for transporting said lubricant from said reservoir intocontact with said balls, whereby lubrication is provided to saidrecirculating ball screw.

2. The ball screw defined in claim 1 wherein said transport meansincludes a porous material incorporated into said recirculating membersuch that lubricant from said reservoir is transported through saidporous material and into contact with said balls as they pass throughsaid tunnel.

3. The ball screw defined in claim 2 wherein said housing comprises asleeve disposed about said nut and includes rings for sealing saidsleeve and said nut to define said reser- 4. The ball screw defined inclaim 2 wherein said recirculating member defines a plurality ofseparate tunnels.

5. The ball screw defined in claim 2 wherein the projection of the ballrecirculation path, defined by said tunnel in said recirculation member,on a surface showing the axial and the circumferential components, is acurve which:

a. at its ends is substantially tangent to the equivalent projection ofthe helical ball path at that point defined by said nut and said screw;

b. curves away from its ends towards its center substantially describingsegments of a cycloid;

c. said cycloid segments being interconnected at their closest points bya straight line substantially tangent to said cycloid segments at saidclosest points.

6. The ball screw defined in claim 1 wherein said recirculating membercomprises a sintered metal.

7. A recirculating ball screw including a lead screw and nut defining ahelical ball path comprising:

a plurality of balls;

a ball recirculating member, coupled to said nut, said member definingat least one ball recirculating path having a pair of openingsterminating in the interior of said nut such that one of said openingsis axially disposed from the other by a space of at least one land, anddefining a path over said land, said openings being shaped so as toapply pressure on said balls urging said bails out of the ball groovesinto said recirculating path and wherein the projections of the saidball recirculation path in said recirculating member on a surface,showing the axial and the circumferential components, is a curve whicha. at its ends is substantially tangent to the equivalent projection ofthe helical ball path at that point defined by said nut and said leadscrew;

b. curves away from its ends toward its center substantially describingsegments of a cycloid;

c. said cycloid segments being interconnected at their closest points bya straight line substantially tangent to said cycloid segments at saidclosest points.

1. A recirculating ball screw including a lead screw and nut defining ahelical ball path, comprising: a plurality of balls; a ballrecirculating member, coupled to said nut, said member defining at leastone tunnel having a pair of openings terminating in the interior of saidnut such that one of said openings is axially disposed from the other bya span of at least one land, said tunnel defining a path over at leastone land of said screw, said openings being shaped so as to applypressure on said balls, urging said balls out of the ball groove intosaid tunnel; a housing disposed about said nut defining an enclosedreservoir for the storage of a lubricant; transport means fortransporting said lubricant from said reservoir into contact with saidballs, whereby lubricAtion is provided to said recirculating ball screw.2. The ball screw defined in claim 1 wherein said transport meansincludes a porous material incorporated into said recirculating membersuch that lubricant from said reservoir is transported through saidporous material and into contact with said balls as they pass throughsaid tunnel.
 3. The ball screw defined in claim 2 wherein said housingcomprises a sleeve disposed about said nut and includes O-rings forsealing said sleeve and said nut to define said reservoir.
 4. The ballscrew defined in claim 2 wherein said recirculating member defines aplurality of separate tunnels.
 5. The ball screw defined in claim 2wherein the projection of the ball recirculation path, defined by saidtunnel in said recirculation member, on a surface showing the axial andthe circumferential components, is a curve which: a. at its ends issubstantially tangent to the equivalent projection of the helical ballpath at that point defined by said nut and said screw; b. curves awayfrom its ends towards its center substantially describing segments of acycloid; c. said cycloid segments being interconnected at their closestpoints by a straight line substantially tangent to said cycloid segmentsat said closest points.
 6. The ball screw defined in claim 1 whereinsaid recirculating member comprises a sintered metal.
 7. A recirculatingball screw including a lead screw and nut defining a helical ball pathcomprising: a plurality of balls; a ball recirculating member, coupledto said nut, said member defining at least one ball recirculating pathhaving a pair of openings terminating in the interior of said nut suchthat one of said openings is axially disposed from the other by a spaceof at least one land, and defining a path over said land, said openingsbeing shaped so as to apply pressure on said balls urging said balls outof the ball grooves into said recirculating path and wherein theprojections of the said ball recirculation path in said recirculatingmember on a surface, showing the axial and the circumferentialcomponents, is a curve which a. at its ends is substantially tangent tothe equivalent projection of the helical ball path at that point definedby said nut and said lead screw; b. curves away from its ends toward itscenter substantially describing segments of a cycloid; c. said cycloidsegments being interconnected at their closest points by a straight linesubstantially tangent to said cycloid segments at said closest points.